The principal objectives of this study are: a. To investigate further the in vivo physpholipid charge compensation mechanism on a subcellular (mitochondrial) level. b. To study the effects on certain membrane-bound enzymes produced when the content of individual phospholipids in the membranes is varied. c. To assess the role of the sphingolipids in this organism and to screen for mutants deficient in these compounds. d. To document the role of the unsaturated fatty acid rhythm in the biological clock. e. To explore further the relationship between the various lipid components in the membranes of Neurospora. To perform these studies, we will employ a unique collection of 13 membrane mutants, many of which do not exist in any other organism. Our collection includes 3 choline requirers, an inositol requirer, a saturated fatty acid requirer, an unsaturated fatty acid requirer, 5 mutants blocked at various steps in steroid synthesis, osmotically sensitive strains, etc. In addition, we will screen some of the existing temperature-sensitive lethal mutants and many of the morphological mutants for possible blocks in impermeable substances, such as cardiolipin and sphingolipid.